By Aarne Heikkila, NBC News

The first thing you notice about Blake Leeper is his megawatt smile. The second thing you notice are his prosthetic legs. Leeper was born without feet, ankles and lower leg bones, a congenital birth defect that's set him apart but never slowed him down.

This weekend, Leeper competes in the 200 meters at the Paralympics Games in London and is a top contender for gold. (He also races in the 100 meters, 400 meters and 4x100-meter relay next week.)

Although he's only been running competitively for three years, he's quickly made a name for himself.

Watch the story tonight on NBC Nightly News.

At the Boiling Point Track Classic in Windsor, Canada, in July, Leeper tied the world record in the Paralympic 100 meters with a run of 10.91 seconds. His motivation, he says, is simple. "Every time I step onto the track, whoever's in the stands, whoever's watching, I'm out to prove to them, and prove to myself that I've done it, I've accomplished something great."

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From left, cameraman Carlos Rigau, Blake Leeper, producer Aarne Heikkila, and correspondent Miguel Almaguer.

Accomplishing the seemingly impossible is nothing new for Leeper. He played basketball and baseball growing up and seems to get pleasure in proving the doubters wrong.

"At birth the doctors said I would never even walk," he says with a grin. 

It is natural to compare Leeper to fellow double below-knee amputee Oscar Pistorius of South Africa, who has blazed trails in competing against able-bodied athletes, most recently at the Olympic Games in London.

At their first head-to-head meeting at the 2011 Paralympic world championships in New Zealand, Leeper came up short, but his coach, Joaquim Cruz, was impressed by what he saw.

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"(Blake) was right there competing with the giant. He wasn't intimated by the world record holder, he just went to compete, and I said, 'I can work with that.'"

Cruz is optimistic about Leeper's chances in London, but no matter the outcome, he says, Blake's already proven to have the heart of a champion.

"This is a kid who not too long ago was not able to run at all," says Cruz. "They gave him a set of legs and three years later, he's breaking world records."